Fix trivial type-check errors in file_manager.

ui/file_manager/file_manager/common/js/externs.js

Index: ui/file_manager/file_manager/common/js/externs.js
diff --git a/ui/file_manager/file_manager/common/js/externs.js b/ui/file_manager/file_manager/common/js/externs.js
new file mode 100644
index 0000000000000000000000000000000000000000..d5f375ee4e382ba80edcbf0a4c9dd6753f8aa25b
--- /dev/null
+++ b/ui/file_manager/file_manager/common/js/externs.js
@@ -0,0 +1,45 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+/**
+ * @constructor
+ * @extends {Window}
+ */
+var BackgroundWindow = function() {};
+
+/**
+ * @type {FileBrowserBackground}
+ */
+BackgroundWindow.prototype.background;
+
+/**
+ * @param {Window} window
+ */
+BackgroundWindow.prototype.registerDialog = function(window) {};
+
+
+/**
+ * @constructor
+ * @extends {Event}
+ */
+var FileOperationProgressEvent = function() {};
+
+/** @type {string} */
+FileOperationProgressEvent.prototype.reason;
+
+/** @type {(FileOperationManager.Error|undefined)} */
+FileOperationProgressEvent.prototype.error;
+
+
+/**
+ * @constructor
+ * @extends {Event}
+ */
+var EntriesChangedEvent = function() {};
+
+/** @type {util.EntryChangedKind} */
+EntriesChangedEvent.prototype.kind;
+
+/** @type {Array.<!Entry>} */
+EntriesChangedEvent.prototype.entries;